Silicone oil is useful for its heat resistance, lubricity, water repellency, gloss retention, mist prevention, antistatic properties, mold release lubricant, corrosion resistance, chemical stability and safety. Utilizing these properties, silicone oil has hitherto been used as bases of compositions in a wide variety of fields including various industrial materials such as textile treating agents, surface lubricants, water repelling agents, resin modifiers, paint additives, electrical insulating agents, heat media, grease, oil for machinery, foam stabilizers and anti-foam agents, pharmaceutical preparations and cosmetics.
In particular, silicone oil has been used as bases of pharmaceutical preparations and cosmetics because of its safety. Usually, low-viscosity silicone oil having a viscosity of 100 cs or less at room temperature is widely used as the bases because of its improved extensibility, refreshing feeling and high safety. However, for example, when a paste-like or grease-like silicone composition is prepared, it is difficult to obtain a smooth, homogeneous composition in a single system, and low-viscosity silicone oil is easily separated or discharged from the resulting composition, resulting in low stability.
In order to solve the above-mentioned problem of low-viscosity silicone oil, there has been proposed the use of organic materials such as the methods of using fatty acid esters of dextrin as thickeners (see Japanese Patent Unexamined Publication Nos. 62-121764, 62-143970, 62-143971 and 63-159489), the methods of using fatty acid esters of sucrose (see Japanese Patent Unexamined Publication No. 63-235366) and the methods of using trimethylsilylated polyvinyl alcohol or trimethylsilylated polysaccharides (see Japanese Patent Unexamined Publication No. 62-240335), and the use of inorganic materials such as the methods of using organically modified viscosity minerals (see Japanese Patent Unexamined Publication Nos. 62-45656, 62-54759 and 63-72779). However, the use of these organic and inorganic materials as the thickeners results in the problem of deteriorating inherent characteristics of low-viscosity silicone oil such as refreshing feeling and extensibility.
Recently, methods have been proposed in which low-viscosity silicone oil is treated using compounds obtained by partially crosslinking silicones having a specific degree of polymerization as thickeners under shearing force, thereby obtaining homogeneous paste-like silicone compositions (see Japanese Patent Unexamined Publication Nos. 2-43263 and 5-140320). However, these methods require the use of mixers such as ball mills, three-roll mills and colloid mills having strong shearing force for obtaining paste-like silicone compositions, resulting in disadvantages such as troublesome preparation, high viscosity of the resulting compositions and restricted compounding amounts of the compositions. Bases have therefore been desired which can make gel and increase viscosity by simpler compounding without impairing the inherent feeling of low molecular weight silicones having a viscosity of 100 cs or less.